New Photosensitizers Based on Heteroleptic Cu(I) Complexes and CO2 Photocatalytic Reduction with (Ni(II)(cyclam))Cl2

Abstract

Summary

A photochemical reduction of CO₂ was shown using the nickel catalyst Ni(cyclam)Cl2 and the copper-based photosensitizers 100906, 100907, 100908 and100909. Turnover numbers (TONs) of 8.1 for CO were reached in acetonitrile/TEOA for complex 100908 after 4 hours. Employing the other synthesized photosensitizers 100906, 100907 or 100909, TONs of 4.3 to 4.9 were obtained. The experiments were conducted under visible-light irradiation (λ = 420 nm) using BIH as sacrificial electron donor (see section SEDs below).

Advances and special progress

The first example of Cu(I)-based photosensitizers used for photocatalytic CO₂ reduction in combination with Ni(cyclam)Cl2 was successfully reported, demonstrating the usability of a fully noble-metal free CO₂ reduction system. The TONs are consistent with previously reported results on noble-metal based photosensitizers.

Additional remarks

The developed heteroleptic photosensitizer complexes showed a high stability in acetonitrile and no ligand release or formation of the homoleptic complexes was detected in UV/Vis stability studies.

Content of the published article in detail

The article contains results for the reduction of CO₂ to CO under visible-light catalysis using a nickel complex as catalyst and copper-based photosensitizers. The catalytic system performs best (referring to the TON of CO production) in acetonitrile/TEOA with photosensitizer 100908.

Catalysts

Ni(cyclam)Cl2

Photosensitizers

100906 100907 100908 100909

Investigations

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	solvent A	.	.	.	.	λexc [nm]	.	TON CO	.
1.	Ni(cyclam)Cl2	0.1	Molecule:100906	1	BIH	0.02	MeCN					420 nm (4 x 8 W)		4.3
2.	Ni(cyclam)Cl2	0.1	Molecule:100907	1	BIH	0.02	MeCN					420 nm (4 x 8 W)		4.9
3.	Ni(cyclam)Cl2	0.1	Molecule:100908	1	BIH	0.02	MeCN					420 nm (4 x 8 W)		8.1
4.	Ni(cyclam)Cl2	0.1	Molecule:100909	1	BIH	0.02	MeCN					420 nm (4 x 8 W)		4.6
5.	Ni(cyclam)Cl2	0.1	Molecule:100906	1	BIH	0.01	MeCN					420 nm (4 x 8 W)		2.6
6.	Ni(cyclam)Cl2	0.1	Molecule:100907	1	BIH	0.01	MeCN					420 nm (4 x 8 W)		3.5
7.	Ni(cyclam)Cl2	0.1	Molecule:100908	1	BIH	0.01	MeCN					420 nm (4 x 8 W)		5.0
8.	Ni(cyclam)Cl2	0.1	Molecule:100909	1	BIH	0.01	MeCN					420 nm (4 x 8 W)		1.8
9.	Ni(cyclam)Cl2	0.1	Molecule:100906	1	BIH	0.01	MeCN					420 nm (4 x 8 W)		2.8
10.			Molecule:100908	1	BIH	0.01	MeCN					420 nm (4 x 8 W)
11.	Ni(cyclam)Cl2	0.1	Molecule:100908	1	BIH	0.01	MeCN					420 nm (4 x 8 W)
12.	Ni(cyclam)Cl2	0.1	Molecule:100908	1			MeCN					420 nm (4 x 8 W)
13.	Ni(cyclam)Cl2	0.1	Molecule:100908	1	BIH	0.01	MeCN					420 nm (4 x 8 W)
14.	Ni(cyclam)Cl2	0.1			BIH	0.01	MeCN					420 nm (4 x 8 W)
15.	Ni(cyclam)Cl2	0.1	Molecule:100906	1	BIH	0.01	MeCN					dark
16.	[Cu(ACN)4][BF4]	0.1	Molecule:100906	1	BIH	0.01	MeCN					420 nm (4 x 8 W)
17.	Ni(cyclam)Cl2	0.1	Molecule:100906	1	BIH	0.02	MeCN					420 nm (4 x 8 W)		7.3
18.	Ni(cyclam)Cl2	0.1	Molecule:100907	1	BIH	0.02	MeCN					420 nm (4 x 8 W)		6.5

Investigation-Name: Photocatalytic CO2 reduction and control experimentsExport

Sacrificial Electron Donor

In this study, the experiments were done with the sacrificial electron donor BIH.

Additives

In this study, TEOA was used as a proton donor. For one experiment, N(Me)3 was employed instead. The catalyst [Cu(ACN)4][BF4] was used for a control experiment.